1. Field of the Invention
The present invention relates to a multi-beam radar sensor having a plurality of antenna elements situated next to each other, a collective lens disposed with distance in front of the antenna element, and an additional preliminary focusing lens, and the present invention also relates to a radar sensor having angular resolution for use in motor vehicles.
2. Description of Related Art
The radar radiation emitted or received by the plurality of antenna elements disposed next to each other passes through the collective lens shared by all antenna elements and is bundled in this manner. However, because of the offset of the individual antenna elements in the lateral direction, the radar beams generated and/or received thereby are likewise angularly offset with respect to each other. If a reflective radar object is hit by multiple beams, then it is possible to determine, or at least estimate, the azimuth angle of the radar object on the basis of the amplitude and/or phase relation between the signals received by the various antenna elements.
The transmission characteristic of such a multi-beam radar sensor is a function of the geometry of the individual antenna elements and the optical characteristics of the collective lens, but is also affected by interference effects between the signals emitted by the different antenna elements.
From published Germany patent document DE 197 55 607, such a radar sensor is known, in which a preliminary focusing lens is disposed in relatively close proximity in front of the antenna element(s). This preliminary focusing lens is dimensioned such that all of the radar radiation that also passes through the actual collective lens traverses it. The preliminary focusing lens is provided to enable a more compact design of the radar sensor.
In the case of a multi-beam sensor, it is also known that there is a proposal to place a cylindrical lens on the planar inner side of the plano-convex collective lens, through which greater bundling than in the azimuth is obtained in the elevation.